After having flashed Kong's DD-WRT, I forcefully bricket my R7800 (pulling the plug while I was flasing the "ddwrt-to-netgear-fw-R7800.bin" from the above link).
Yes, other than one or two blinking lights, it was a great paperwieght for a few minutes.

if the gui version of tftp2 fails which happens sometimes, initiate the transfer from a cmd window "tftp -i 192.168.1.1 put r7800xxxx.img" replace r7800xxxx.img with the actual firmware name, minus the quotes